The present invention relates to a silver halide photographic material and an image formation method using the same, and particularly to a heat developable silver halide photographic material (silver halide photothermographic material) and an image formation method using the same.
In the field of silver halide photographic materials, the so-called color diffusion transfer process is known in which diffusible dyes are formed imagewise and fixed to image receiving materials, thereby forming color images. With respect to this process, many proposals have been made.
In this process, the diffusible dyes are generally produced as a function of development of silver halides from compounds obtained by making previously colored image formation dyes (preformed dyes) diffusion-resistant (such compounds are hereinafter referred to as xe2x80x9ccoloring materials). Accordingly, the addition of the coloring materials to layers having silver halide emulsions causes an undesirable reduction in sensitivity to exposure because of the filter effect due to dye moieties. For avoiding this problem, the coloring materials for image formation are generally added to layers apart from exposure faces of silver halide emulsion layers. This process can avoid the reduction in sensitivity caused by the filter effect, but has the disadvantage that an increase in the distance between the silver halide emulsions and the coloring materials producing the diffusible dyes causes inefficient transfer of development information from the silver halide emulsion to the coloring materials.
For improving these disadvantages, a so-called coupling system has been proposed in which dye formation is carried out by the coupling reaction of oxidation products of developing agents with couplers. This system can advantageously overcome the disadvantages of the system using the preformed dyes, because both the developing agents and the couplers are colorless. This system is therefore more preferred than the use of the coloring materials utilizing the preformed dyes. This process is described, for example, in U.S. Pat. No. 4,469,773 and JP-B-63-36487 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d).
However, when the photographic materials contain the color developing agents for the above-mentioned coupling system, the sufficient keeping stability is insufficiently compatible with the activity of the coupling reaction.
Recently, a technique of forming diffusible dyes using color developing agents of the hydrazine family has been developed, and is described in JP-A-9-152705 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). However, compounds described herein have the problem that they are low in the color generation of cyan or magenta, or that the dyes produced are low in light fastness.
An object of the invention is to provide a silver halide photographic material excellent in color generation in development.
Another object of the invention is to provide a silver halide photographic material excellent in color reproducibility.
A further object of the invention is to provide a silver halide photographic material excellent in color image fastness, particularly, in light fastness.
A still further object of the invention is to provide a silver halide photographic material excellent in color image fastness, particularly, in light fastness at low density areas.
A still further object of the invention is to provide an image formation method using a silver halide photographic material excellent in the above-mentioned characteristics.
According to the invention, there are provided silver halide photographic materials and image formation methods having the following constitution, thereby attaining the above-mentioned objects.
(1) A silver halide photographic material comprising at least one coupler represented by the following formula (Ia): 
wherein R1 represents an alkyl group which may be optionally substituted, with the proviso that an alkyl group substituted by a halogen atom alone and an alkyl group substituted by a halogen atom and an aryl group are excluded from R1; R2 and R3, which may be the same or different, each represents a hydrogen atom or a substituent; and X1 represents a group which can leave by coupling with an oxidation product of a color developing agent;
(2) The silver halide photographic material described in (1), wherein R1 of formula (Ia) is a tertiary alkyl group;
(3) The silver halide photographic material described in (1) or (2), wherein R2 of formula (Ia) is an acylamino group, an alkoxycarbonylamino group or an ureido group;
(4) A silver halide photographic material comprising at least one coupler represented by the following formula (II): 
wherein R4 represents a tertiary alkyl group; R5 represents a substituent; and X2 represents a group leaving by coupling (a coupling-off group) which is linked by an oxygen atom to a mother nucleus of a phenol coupler and has a formula weight of 200 or more;
(5) The silver halide photographic material described in (4), wherein at least one of R4 and R5 of formula (II) is a group having a dissociative group with a pKa of 1 to 12;
(6) A silver halide photographic material comprising a support having provided thereon at least one hydrophilic colloidal layer containing at least one coupler represented by the following formula (Ib) and at least one color developing agent represented by the following formula (III): 
wherein R1 represents an alkyl group which may be optionally substituted; R2 and R3, which may be the same or different, each represents a hydrogen atom or a substituent; and X1 represents a group which can leave by coupling with an oxidation product of a color developing agent, 
wherein Cxcex1 represents a carbon atom; Z represents a carbamoyl group, an acyl group, an alkoxycarbonyl group or an aryloxycarbonyl group; and Q represents an atomic group forming an unsaturated ring together with Cxcex1;
(7) A heat developable silver halide photographic material (a silver halide photothermographic material) comprising at least one coupler represented by the following formula (IV): 
wherein R11 represents an acylamino group or an alkyl group; R12 and R13 each independently represents a hydrogen atom or a substituent; A represents a nitrogen atom or an oxygen atom; when A is an oxygen atom, m represents 0; when A is a nitrogen atom, M represents a xe2x80x94COxe2x80x94 group or an xe2x80x94SO2xe2x80x94 group; R14 represents an alkyl group, an aryl group, an alkoxyl group or an amino group, and m represents 1; xe2x80x94A(H)xe2x80x94(Mxe2x80x94R14)m may be cyclocondensed with a benzene ring to form a 5-, 6- or 7-membered ring; R15 represents a substituent, and n represents an integer of 0 to 4; and X11 represents a group which can leave by coupling with an oxidation product of a color developing agent;
(8) The heat developable silver halide photographic material described in (7), wherein R11 of formula (IV) is a tertiary alkyl group;
(9) The heat developable silver halide photographic material described in (7) or (8), wherein R11 of formula (IV) is a tertiary alkyl group, R12 is a hydrogen atom, and R13 is a hydrogen atom, a halogen atom, an alkoxy group, an acylamino group, an alkoxycarbonylamino group or a carbamoylamino group;
(10) The heat developable silver halide photographic material described in (7) or (8), wherein R11 of formula (IV) represents a tertiary alkyl group, A represents a nitrogen atom, M represents a xe2x80x94COxe2x80x94 group or an xe2x80x94SO2xe2x80x94 group, R14 represents an alkyl group or an aryl group, m represents 1, R12 and R13 each represents a hydrogen atom, R15 represents a substituent, n represents an integer of 0 to 4, and X11 represents a group leaving by coupling which is linked by an oxygen atom to a mother nucleus of a phenol coupler and has a formula weight of 200 or more;
(11) A heat developable silver halide photographic material comprising a support having provided thereon at least one hydrophilic colloidal layer containing at least one coupler represented by formula (IV) and at least one color developing agent represented by the following formula (III): 
wherein Cxcex1 represents a carbon atom; Z represents a carbamoyl group, an acyl group, an alkoxycarbonyl group or an aryloxycarbonyl group; and Q represents an atomic group forming an unsaturated ring together with Cxcex1;
(12) An image formation method comprising heat developing the silver halide photographic material described in (1) or (7); and
(13) An image formation method comprising developing the silver halide photographic material described in (1) or (7) by developing an alkali processing solution.
The couplers represented by formulas (Ia) and (Ib) (formulas (Ia) and (Ib) are both described as formula (I) in the following description), which are used in the invention, will be illustrated in detail below.
In formula (I), R1 represents an alkyl group. The alkyl group is a straight-chain, branched or cyclic alkyl group having from 1 to 50 carbon atoms (e.g., methyl, ethyl, isopropyl, t-butyl, t-pentyl, cyclopropyl, cyclohexyl, 2-ethylhexyl or dodecyl). The alkyl group is preferably a secondary or tertiary alkyl group, more preferably a tertiary alkyl group, and most preferably a t-butyl group. The number of carbon atoms thereof is preferably from 1 to 8, more preferably from 1 to 5, and most preferably from 1 to 4.
R1 may have a substituent other than a halogen atom. Examples of the substituents include straight-chain, branched or cyclic alkyl groups each having from 1 to 50 carbon atoms (e.g., trifluoromethyl, methyl, ethyl, propyl, heptafluoro-propyl, isopropyl, butyl, t-butyl, t-pentyl, cyclopentyl, cyclohexyl, octyl, 2-ethylhexyl and dodecyl), straight-chain, branched or cyclic alkenyl groups each having from 2 to 50 carbon atoms (e.g., vinyl, 1-methylvinyl and cyclohexene-1-yl), alkynyl groups each having a total carbon number of 2 to 50 (e.g., ethynyl and 1-propynyl), aryl groups each having from 6 to 50 carbon atoms (e.g, phenyl, naphthyl and anthryl), acyloxy groups each having from 1 to 50 carbon atoms (e.g., acetoxy, tetradecanoyloxy and benzoyloxy), carbamoyloxy groups each having from 1 to 50 carbon atoms (e.g., N,N-dimethylcarbamoyloxy), carbonamido groups each having from 1 to 50 carbon atoms (e.g., formamido, N-methylacetamido, acetamido, N-methylformamido and benzamido), sulfonamido groups each having from 1 to 50 carbon atoms (e.g, methanesulfonamido, dodecanesulfonamido, benzene-sulfonamido and p-toluenesulfonamido), carbamoyl groups each having from 1 to 50 carbon atoms (e.g, N-methylcarbamoyl, N,N-diethylcarbamoyl and N-mesylcarbamoyl, sulfamoyl groups each having from 0 to 50 carbon atoms (e.g., N-butyl-sulfamoyl, N,N-diethylsulfamoyl and N-methyl-N-(4-methoxyphenyl)sulfamoyl), alkoxy groups each having from 1 to 50 carbon atoms (e.g, methoxy, propoxy, isopropoxy, octyloxy, t-octyloxy, dodecyloxy and 2-(2,4-di-t-pentylphenoxy)ethoxy), aryloxy groups each having from 6 to 50 carbon atoms (e.g., phenoxy, 4-methoxyphenoxy and naphthoxy), aryloxycarbonyl groups each having from 7 to 50 carbon atoms (e.g., phenoxycarbonyl and naphthoxycarbonyl), alkoxycarbonyl groups each having from 2 to 50 carbon atoms (e.g., methoxycarbonyl and t-butoxycarbonyl), N-acylsulfamoyl groups each having from 1 to 50 carbon atoms (e.g., N-tetradecanoylsulfamoyl and N-benzoylsulfamoyl), alkylsulfonyl groups each having from 1 to 50 carbon atoms (e.g., methane-sulfonyl, octylsulfonyl, 2-methoxyethylsulfonyl and 2-hexyldecylsulfonyl), arylsulfonyl groups each having from 6 to 50 carbon atoms (e.g., benzenesulfonyl, p-toluenesulfonyl and 4-phenylsulfonyl), alkoxycarbonylamino groups each having from 2 to 50 carbon atoms (e.g., ethoxycarbonylamino), aryloxycarbonylamino groups each having from 7 to 50 carbon atoms (e.g., phenoxycarbonylamino and naphthoxycarbonyl-amino), amino groups each having from 0 to 50 carbon atoms (e.g., amino, methylamino, diethylamino, diisopropylamino, anilino and morpholino), a cyano group, a nitro group, a carboxyl group, a hydroxyl group, a sulfo group, a mercapto group, alkylsulfinyl groups each having from 1 to 50 carbon atoms (e.g., methanesulfinyl and octanesulfinyl), aryl-sulfinyl groups each having from 6 to 50 carbon atoms (e.g., benzenesulfinyl, 4-chlorophenylsulfinyl and p-toluenesulfinyl), alkylthio groups each having from 1 to 50 carbon atoms (e.g., methylthio, octylthio and cyclohexylthio), arylthio groups each having from 6 to 50 carbon atoms (e.g., phenylthio and naphthylthio), ureido groups each having from 1 to 50 carbon atoms (e.g., 3-methylureido, 3,3-dimethyl-ureido and 1,3-diphenylureido), heterocyclic groups each having from 2 to 50 carbon atoms (3- to 12-membered monocyclic or condensed rings each containing, for example, at least one atom, preferably from 1 to 9 atoms, of nitrogen, oxygen and sulfur atoms as heteroatoms, for example, 2-furyl, 2-pyranyl, 2-pyridyl, 2-thienyl, 2-imidazolyl, morpholino, 2-quinolyl, 2-benzimidazolyl, 2-benzothiazolyl and 2-benzoxazolyl), acyl groups each having from 1 to 50 carbon atoms (e.g., acetyl, benzoyl and trifluoroacetyl), sulfamoyl-amino groups each having from 0 to 50 carbon atoms (e.g., N-butylsulfamoylamino and N-phenylsulfamoylamino), silyl groups each having from 3 to 50 carbon atoms (e.g., trimethylsilyl, dimethyl-t-butylsilyl and triphenylsilyl). The above-mentioned substituents may further have substituents, and examples of the substituents include the substituents mentioned above.
In formula (I), R2 is a hydrogen atom or a substituent. Examples of the substituents include halogen atoms and ones mentioned above as the examples of the substituents which R1 may have.
R2 is preferably a hydrogen atom, a halogen atom, an acylamino group, an alkoxycarbonylamino group, an aryl-oxycarbonylamino group or an ureido group, and more preferably an acylamino group, an alkoxycarbonylamino group or an ureido group.
In formula (I), R3 is a hydrogen atom or a substituent. Examples of the substituents include halogen atoms and ones mentioned above as the examples of the substituents which R1 may have. R3 is preferably a hydrogen atom.
In formula (I), it is preferred that at least one of R1, R2 and R3 has a dissociative group with a pKa of 1 to 12. It is more preferred that R2 has the dissociative group. The pKa of the dissociative group is more preferably from 3 to 12, and most preferably from 5 to 11.
Preferred examples of the dissociative groups include an xe2x80x94NHSO2xe2x80x94 group, phenolic hydroxyl groups, a xe2x80x94CONHCOxe2x80x94 group, a xe2x80x94CONHSO2xe2x80x94 group and groups containing xe2x80x94CON(R)xe2x80x94OH (wherein R represents a hydrogen atom or a substituent, and is preferably an alkyl group, an aryl group or a heterocyclic group), xe2x80x94COOH or xe2x80x94SO2NHSO2xe2x80x94. The xe2x80x94NHSO2xe2x80x94 group, the phenolic hydroxyl groups, the xe2x80x94CONHCOxe2x80x94 group, the xe2x80x94CONHSO2xe2x80x94 group and the xe2x80x94SO2NHSO2xe2x80x94 group are more preferred.
In formula (I), X1 represents a group which can leave by a coupling reaction with an oxidation product of a developing agent. X1 is, for example, a heterocyclic group (a saturated or unsaturated, 5-, 6- or 7-membered monocyclic or condensed ring containing at least one atom of nitrogen, oxygen and sulfur as a heteroatom). Examples thereof include succinimide, maleinimide, phthalimide, diglycollimide, pyrrole, pyrazole, imidazole, 1,2,4-triazole, tetrazole, indole, benzopyrazole, benzimidazole, benzotriazole, imidazoline-2,4-dione, oxazolidine-2,4-dione, thiazolidine-2,4-dione, imidazolidine-2-one, oxazoline-2-one, thiazoline-2-one, benzimidazoline-2-one, benzoxazoline-2-one, benzothiazoline-2-one, 2-pyrroline-5-one, 2-imidazoline-5-one, indoline-2,3-dione, 2,6-dioxypurine, parabanic acid, 1,2,4-triazolidine-3,5-dione, 2-pyridone, 4-pyridone, 2-pyrimidone, 6-pyridazone, 2-pyrazone, 2-amino-1,3,4-thiazolidine, 2-imino-1,3,4-thiazolidine-4-one, halogen atoms (e.g., chlorine and bromine), aryloxy groups (e.g., phenoxy and 1-naphthoxy), heterocyclic oxy groups (e.g., pyridyloxy and pyrazolyloxy), acyloxy groups (e.g., cyclohexylcarbonyl-oxy and benzoyloxy), alkoxy groups (e.g., methoxy, ethoxy and dodecyloxy), carbamoyloxy groups (e.g., N,N-didodecyl-carbamoyloxy and morpholinocarbonyloxy), aryloxycarbonyloxy groups (e.g., phenoxycarbonyloxy), alkoxycarbonyloxy groups (e.g., methoxycarbonyloxy and hexadecylcarbonyloxy), arylthio groups (e.g., phenylthio and naphthylthio), heterocyclic thio groups (e.g., tetrazolylthio, 1,3,4-thiadiazolylthio, 1,3,4-oxadiazolylthio and benzimidazolylthio), alkylthio groups (e.g., methylthio, octylthio and hexadecylthio), alkylsulfonyloxy groups, arylsulfonyloxy groups (e.g., benzenesulfonyloxy and toluenesulfonyloxy), carbonamido groups (e.g., undecylcarbonylamino and phenylcarbonylamino), sulfonamido groups (e.g., dodecylsulfonamido and benzenesulfonamido), alkylsulfonyl groups, arylslufonyl groups (e.g., benzenesulfonyl), alkylsulfinyl groups (e.g., octylsulfinyl), arylsulfinyl groups (e.g., benzenesulfinyl) and carbamoylamino groups (e.g., N-hexadecylcarbamoylamino).
Of these, preferred are the aryloxy groups, the heterocyclic oxy groups, the acyloxy groups, the alkoxy-carbonyloxy groups, the carbamoyloxy groups, the aryloxy-carbonyloxy groups, the arylthio groups, the heterocyclic thio groups, the alkylsulfonyloxy groups and the aryl-sulfonyloxy groups, and more preferred are the aryloxy groups, the heterocyclic oxy groups, the acyloxy groups, the aryloxycarbonyloxy groups, the alkoxycarbonyloxy groups and the carbamoyloxy groups.
X1 may be substituted by a substituent. Examples of the substituents for X1 include halogen atoms and ones mentioned above as the examples of the substituents which R1 may have.
The formula weight of X1 is preferably 200 or more, and more preferably 250 or more.
In formula (II), R4 is a straight-chain or cyclic tertiary alkyl group having from 4 to 50 carbon atoms, and preferably a t-butyl group. R4 may be substituted by a substituent. Examples of the substituents include halogen atoms and ones mentioned above as the examples of the substituents which R1 may have. R4 has preferably from 4 to 8 carbon atoms, and more preferably 4 or 5 carbon atoms.
In formula (II), R5 represents a hydrogen atom or a substituent. Examples of the substituents include halogen atoms and ones mentioned above as the examples of the substituents which R1 may have. R5 is preferably an alkyl group, an aryl group, a heterocyclic group, an alkoxy group, an aryloxy group, an amino group or an anilino group.
In formula (II), it is preferred that at least one of R4 and R5 has a dissociative group with a pKa of 1 to 12. It is more preferred that R2 has the dissociative group.
The pKa of the dissociative group is more preferably from 3 to 12, and most preferably from 5 to 11.
Preferred examples of the dissociative groups include an xe2x80x94NHSO2xe2x80x94 group, phenolic hydroxyl groups, a xe2x80x94CONHCOxe2x80x94 group, a xe2x80x94CONHSO2xe2x80x94 group and groups containing xe2x80x94CON(R)xe2x80x94OH (wherein R represents a hydrogen atom or a substituent, and is preferably an alkyl group, an aryl group or a heterocyclic group), xe2x80x94COOH or xe2x80x94SO2NHSO2xe2x80x94. The xe2x80x94NHSO2xe2x80x94 group, the phenolic hydroxyl groups, the xe2x80x94CONHCOxe2x80x94 group, the xe2x80x94CONHSO2xe2x80x94 group and the xe2x80x94SO2NHSO2xe2x80x94 group are more preferred.
In formula (II), X2 represents a group which is linked by an oxygen atom to a mother nucleus of a phenol coupler, and which can leave by a coupling reaction with an oxidation product of a color developing agent.
The formula weight of X2 is 200 or more, and preferably 250 or more.
X2 is preferably an acyloxy group having from 1 to 50 carbon atoms, an alkoxy group having from 1 to 50 carbon atoms, an aryloxy group having from 6 to 50 carbon atoms, a heterocyclic oxy group having from 1 to 50 carbon atoms, an alkoxycarbonyloxy group having from 2 to 50 carbon atoms, an aryloxycarbonyloxy group having from 7 to 50 carbon atoms, a carbamoyloxy group having from 1 to 50 carbon atoms or a heterocyclic carbonyloxy group having from 2 to 50 carbon atoms. More preferably, X2 is the carbamoyloxy group or the alkoxycarbonyloxy group. X2 may have a substituent, and examples of the substituents include halogen atoms and ones mentioned above as the examples of the substituents which R1 may have.
Specific examples of the couplers represented by formula (I) or (II) are shown below, but the scope of the invention is not limited to these specific examples. 